The deep peroneal nerve is a small branch of the common peroneal nerve. The deep peroneal nerve innervates the web space between the first and second toes. The nerve crosses over the anterior tibial artery from medial to lateral just proximal to the ankle joint near the surface of the distal tibia. The deep peroneal nerve can appear as a homogeneous hypoechoic structure surrounded by hyperechoic fat without polyfascicular echotexture. The deep peroneal nerve is more difficult to image in the proximal leg.¹ This probably relates to the course of the nerve and its division into a large number of motor branches.²

Ultrasound guidance may provide some advantages over landmark-based approaches to deep peroneal nerve block. One study reported the use of ultrasound improved the onset of deep peroneal nerve block at the ankle although the overall quality of this block was no different.³ Another study has reported high success rates with deep peroneal nerve blocks that combine ultrasound with nerve stimulation.⁴

Suggested Technique

The deep peroneal nerve and anterior tibial artery lie between the surface of the tibia and the extensor hallucis longus muscle. Because of its superficial location and proximity to bone, the anterior tibial artery is easily compressed by the transducer over the dorsum of the foot and ankle. Light touch with the transducer is necessary to image the anterior tibial artery. By sliding the transducer back and forth from proximal to distal, the crossing of the deep peroneal nerve over the anterior tibial artery can be identified. Both in-plane and out-of-plane approaches are useful for this block. In-plane approach from lateral to medial avoids the large tibialis anterior and extensor hallucis longus tendons. Furthermore, the deep peroneal nerve is most likely to lie on the lateral side of the anterior tibial artery.

Key Points

Deep Peroneal Nerve Block	The Essentials
Anatomy	The DPN often crosses over the AT.
	This crossing point is near where the AT lies on the surface of the tibia.
Positioning	Supine
Operator	Standing on the side of the patient
Display	Across the table
Transducer	High-frequency linear, 23- to 38-mm footprint
Initial depth setting	20 mm
Needle	25 gauge, 38 mm in length
Anatomic location	Begin by scanning between the malleoli over the dorsum of the foot.
	Slide the probe proximal and distal to identify the DPN and AT.
	Light touch is needed to avoid compressing the AT.
Approach	SAX view of DPN, in-plane from lateral to medial
	Place the needle tip between the DPN and AT.
Sonographic assessment	The injection should separate the DPN and AT.
Anatomic variation	The DPN can divide into medial and lateral branches proximally.

AT, Anterior tibial artery; DPN, deep peroneal nerve; SAX, short axis.

Clinical Pearls

• Because the deep peroneal nerve is small, it is difficult to visualize where it branches off from the common peroneal nerve in the proximal leg.

• The point at which the deep peroneal nerve crosses over the anterior tibial artery is typically proximal to the ankle joint where the artery lies on the surface of the tibia.

• The deep peroneal nerve divides into medial and lateral branches. These branches lie on their respective sides of the anterior tibial artery.

• The deep peroneal nerve can be blocked by peeling off the nerve from the anterior tibial artery where it lies in the 12-o’clock position with respect to the artery (at the crossing point). The injection should separate the deep peroneal nerve from the surface of the anterior tibial artery.

FIGURE 47-1 Course of the deep peroneal nerve.

(Adapted from Drake RL, Vogl W, Mitchell AWM. Gray’s anatomy for students. Philadelphia: Churchill Livingstone; 2004.)

FIGURE 47-2 External photograph showing the approach to deep peroneal block in the distal leg. An in-plane approach from the lateral aspect of the leg is shown (A). The corresponding sonogram is shown before needle placement (B). The deep peroneal nerve crosses over the surface of the anterior tibial artery proximal to the ankle joint.

FIGURE 47-3 Short-axis view of the deep peroneal nerve over the dorsum of the foot. In this more distal location, the metatarsal bones lie under the nerve. This location is too distal for complete block.

FIGURE 47-4 Image sequence showing deep peroneal nerve block in the distal leg. At this location the deep peroneal nerve lies over the anterior tibial artery. An in-plane approach is demonstrated in which the needle tip is placed adjacent to the anterior tibial artery and the deep peroneal nerve with the nerve in the 12-o’clock position (A). After injection, local anesthetic is distributed around the deep peroneal nerve and begins to separate the nerve from the artery (B), also shown at higher magnification (C).

FIGURE 47-5 Image sequence showing deep peroneal nerve block in the distal leg. At this location the deep peroneal nerve lies on the side of the anterior tibial artery. An in-plane approach is demonstrated in which the needle tip is placed under the deep peroneal nerve (A). After injection the local anesthetic lifts the nerve from the surface of the bone (B).